NASA to crash tiny probes into Mars at 400 mph

Posted: Monday, November 29, 1999

MATTHEW FORDAHLAP Science Writer

PASADENA, Calif. - Two little space probes heading for Mars this week won't float beneath parachutes or bounce to a landing on cushions. Instead, they'll smash into the planet at 400 mph, punching into the ground like interplanetary lawn darts.

If the drastic landing technique works Friday, the softball-size instrument packages will search for water and test lower-cost technology that could revolutionize solar system exploration.

The Deep Space 2 probes are flying toward the Red Planet along with the Mars Polar Lander.

After they reach Mars, Polar Lander will begin a controlled descent. The probes will follow 18 seconds later, but unlike the lander, their 77-mile fall won't be slowed by any expensive parachutes or thrusters.

The $29.6 million Deep Space 2 probes are part of NASA's New Millennium program, a series of inexpensive missions testing untried technology for future spacecraft. Ten systems will be tried out during the Mars mission.

For four years, Gavit and her team have been throwing models out of airplanes over the Mojave Desert and firing electronic devices out of air guns to find designs and materials that might survive a crash into the surface.

After about 20 attempts, they finally arrived at a design that should withstand the force of impact, which will be 60,000 times stronger than gravity on Earth.

Each probe will be protected from the heat of entry by a basketball-size aeroshell, but that will shatter when it hits the surface.

Impact will cause a bullet-like penetrator to separate from the center of each probe and plunge up to 2 feet into the ground. A cable will connect the penetrator to the orange aboveground unit that contains instruments and a transmitter.

Even after successful tests on Earth, there's no guarantee of survival on Mars. The 8-pound probes might hit rocks and shatter. Their antennas could be swallowed up by soft, dusty soil. A gust of wind could blow them upside down during flight.

"We've got a pretty robust design, but it's like throwing one of these things out here in the middle of Pasadena and saying it has got to penetrate no matter where it lands," Gavit said. "If it lands in the middle of the freeway, it's not going to penetrate."

The probes should hit the surface about a mile from each other and 35 miles from the lander in an area 500 miles from the planet's south pole.

Deep Space 2 will be declared a success if mission controllers receive any signal from one of the probes. Any science data will be considered a windfall, said Suzanne Smrekar, project scientist for Deep Space 2.

During descent and impact, instruments will record acceleration for a study of the density of the atmosphere and the surface. Thermometers will show how quickly each probe cools - measurements that can be used to search for water.

But the main water experiment is the most ambitious: After the penetrator stops, a small drill will collect an eraser-size soil sample that will be heated and tested by a laser for evidence of water vapor.

"The water experiment requires a motor to run, a drill to extend. In all the tests, everything worked out," she said. "We're expecting it to work. But it certainly by far requires more things to go properly than any of the other experiments."

Most of the experiments will be completed within an hour and data returned late Friday. The probes should continue measuring soil temperature for two to three days.

Gavit said she hopes everything works. If not, there's always her other job - planning an interstellar mission.

"I'm going from a crazy program to something that's really crazy," she said.